Michael Bayne
3e8ac68af6
initialValue=N) for non-zero values of N. This is complicated. Depot used to
"initialize" value generators pretty much every time a table schema was
migrated. For TableValueGenerator it could just NOOP if the proper row was in
the sequence table. IdentityValueGenerator was just broken and ignored any
request to configure an initialValue, so it never did anything.
First I looked into preserving this frequent reinitialization behavior, but it
turns out that it's not possible to read the current value of a sequence in
Postgres without modifying it. So trying to do something like:
SELECT setval('"FooRecord_fooId_seq"', max(currval('"FooRecord_fooId_seq"'),
cast(initialValue as bigint)));
doesn't work because you can't call currval() without first having called
nextval() (and furthermore when you do that, the Postgres client grabs a block
of sequence values for this client so that multiple clients can add rows to a
table without having to coordinate with the server and one another to assign a
new value every time a row is inserted).
So I changed Depot around to not reinitialize value generators unless it really
believes that the column in question is newly added. We can't rely on our own
auto-column creation because it's possible for someone to create a column
through a custom entity migration, so instead we just keep track of what
columns we had before we started all of our migrations (automatic and custom)
and check to see if there are any new columns after all is said and done and if
any of those have value generators, we "create" them.
This allows us to just setval() the sequence to the desired initial value
without first reading it.
This all fails if someone renames a column with a value generator. The column
will appear to Depot to be new and it will try to recreate the value generator
on that column. For TableValueGenerators that will basically NOOP and
everything will be just like it was before. For IdentityValueGenerators,
because of the way that Postgres magically creates a tablename_columnname_seq
sequence for identity value generation, when the column is renamed, the
sequence will retain the old column name and when Depot goes to try to setval()
the sequence based on the new column name, it won't exist and the migration
will fail. So at least we're not silently reinitializing the value generator to
its initial value when a column (with an identity value generator) is renamed.
We also don't try to do anything if the initialValue is not 1 (the default). So
we avoid failing or doing anything wrong if those kinds of columns are renamed.
So we only fail if someone renames a column with an identity value generator
with a non-default initial value. Since one can only put a value generator on a
primary key field and an identity value generator generally means you have
something simple like FooRecord with fooId. This means someone is renaming
their simple auto incrementing primary key field which seems extremely unlikely
because those columns usually have an obvious name that you're never going to
change. No problem!
I also haven't fixed this problem for MySQL yet. I can only handle so much
database befuckaroundery in one go.